Here is my 2 1/2 year old in a forward facing car seat and my 4 1/2 year old in a booster seat. Last year they were both in forward facing car seats. No problem for them to climb in and out of the back seat. The passenger seat extenders are a must have so I can climb back there and get them buckled in.
Cute kids.
As a fellow parent, I would recommend getting a head rest for your daughters seat. That can be very dangerous in a collision.